1. Field of the Invention
This invention is generally related to grinding apparatus, and more specifically to a relatively small scale, reasonably priced method and apparatus for comminuting a wide variety of different kinds of materials.
2. Brief Description of the Prior Art
Grinding mills have been utilized for many years in a variety of applications. For example, grinding mills have been commonly used in the past for grinding grains, corn, hay, and other forage materials for livestock feed, as well as paper for cellulose insulation and other commercial uses. Many varieties of grinding mills for comminuting such materials have been developed, such as stone mills, burr mills, hammer mills, and roller mills. However, few, if any, reasonably priced and reasonably sized grinders are available that can handle effectively and efficiently a variety of different kinds of materials, for example, ranging from grains to forage to wood.
Because forage materials and wood, including tree branches, tend to be fibrous and stalky, hammer mill type grinders have been found to be the most effective in comminuting these forage or roughage materials. However, handling and feeding these bulky, fibrous, stalky materials into a hammer mill in a uniform manner proved to be quite difficult and required a good deal of tedious manual labor, because they do not flow in a uniform manner like grains.
Some of the more successful recent developments in grinding apparatus to alleviate the problems in feeding bulky, fibrous, and stalky materials into hammer mills include the relatively large grinders now known generically as tub grinders because of the characteristic rotating tub-shaped feeders. Tub grinders were designed initially to feed very large bales of hay and other forage materials into hammer mill apparatus without the need for excessive manual labor. In a typical tub grinder, the hammer mill cylinder is positioned under and extends partially through the floor or bottom of the tub, and the rotating tub feeds the bottom of the bale or pile of material to be comminuted over the hammer mill. The hammers on the hammer mill cylinder rotate at a high angular velocity and chew off the forage on the bottom of the bale as the base of the bale rotates over the hammer mill cylinder in the floor of the tub. Typical examples of such tub grinders can be found in the following patents: U.S. Pat. No. 2,650,745, issued to W. Oberwortman, U.S. Pat. No. 3,615,059, issued to E. Moeller; U.S. Pat. No. 3,743,191, issued to R. Anderson; U.S. Pat. No. 3,912,175, issued to R. Anderson; U.S. Pat. No. 3,966,128, issued to J. Anderson, et al.; U.S. Pat. No. 4,003,502, issued to E. Barcell; U.S. Pat. No. 4,087,051, issued to C. Moeller; and U.S. Pat. No. 4,106,706, issued to H. Burrows.
Tub grinders have been found to be quite effective for grinding not only large bales of hay, but also for grinding large quantities of forage or roughage materials. Therefore, with the exception of expensive, large, stationary grinders in more or less permanent industrial grinding installations with special, custom designed conveyors and other feed apparatus for specific purposes, the tub grinders have become somewhat of a standard for larger, portable, mid-priced, general purpose grinding machines. Consequently, when recent environmental ordinances and regulations began to prohibit dumping of bulk, unprocessed yard wastes, grass clippings, branches, construction waste, paper, and the like into community landfills, the larger operators began to use tub grinders for comminuting such materials before hauling them to landfills. Such tub grinders have now been used with marginal success for comminuting such bulky materials, which are commonly referred to as commercial or industrial waste, where large quantities of such materials have to be handled, and particularly where the materials are dumped into the hammer mill in batches. In response to this need, several manufacturers have now started making special, heavy duty tub grinders for comminuting such commercial and industrial wastes, because the conventional agricultural tub grinders made for grinding hay proved to be too light, and they break down or wear out too fast when used for comminuting such commercial and industrial wastes.
While the tub grinders and other specialized grinder apparatus are filling a need for large-scale users, as described above, they are too large and expensive to meet the needs of small-scale users, who are also required to comminute their yard wastes, grass clippings, branch prunings, waste wood, leaves, waste paper, assorted rubbish, and the like into more readily decomposable form before dumping them into community landfills or using them as compost materials. Therefore, there is a steadily increasing need for an economical, light-duty, commercial grinder or miller that is capable of grinding such materials more reliably and efficiently. Such a grinder should be capable of reliably grinding all types of shreddable or comminutable materials such as paper, cardboard, clay, wood, branches, yard waste, bark, wet leaves, grass clippings, weeds, plastic, tin and aluminum cans, and other common waste materials, yet not jam when certain non-comminutable material, such as chunks of metal, rock, or concrete might accidently find their way into the mill. Because small-scale users, such as landscapers, grounds keepers, and the like also often need to grind hay or straw for compost or for ground cover in newly seeded areas, the grinder should also be able to handle those kinds of needs. It would be even more beneficial if it could also handle rubbish and even grains for users who have a variety of needs.
Further, because of the varying nature of the homogeneity of such a wide variety of materials, from the irregular and stocky nature of branches, to the dense, resilient nature of wet paper and grass, to small, uniformly sized kernels of grain, the grinder should be capable of reliably and evenly feeding quantities of such materials uniformly and efficiently into the hammer mill rotor for comminuting all such materials to desired particle sizes and consistencies. There are smaller scale grinding machines available for each such special purpose. For example, there are small scale wood chippers available for handling branches. There are hammer mills available for handling hay or straw. There are also hammer mills available for handling grains. However, there are few, if any, hammer mills available for handling wet leaves, grass clippings, and waste paper, and there has not been any single machine available that can handle reliably and comminute efficiently and effectively a wide variety of such materials on a reliable small or light duty scale. The U.S. Pat. No. 4,773,601, developed by one of the joint inventors of the grinder in the present patent application was an attempt to do so by providing a small-scale rotating tub feeder that was interchangeable with a hand-feeder chute for branches. While that small-scale tub grinder and wood chipper combination has some useful features and solved some significant problems, there are still shortcomings. For example, the small rotating tub just does not work as well as large tubs for feeding wet leaves, grass clippings, hay, straw, waste paper, and the like. It tends to bridge or to feed in slugs, rather than a smooth, even feed, and the feed roller tends to fill and clog with wet leaves and muddy grass clippings. The small tub is also too small for receiving batch dumps of such materials from a front end loader or similar machines that are normally used for handling such materials in smaller or medium scale commercial operations. Also, the chute is only good for hand-feeding branches and wood into the grinder. The comminuting mechanism itself of the grinder in U.S. Pat. No. 4,773,601 also has some deficiencies. For example, the aligned hammers tend to carve grooves in larger branches and pieces of wood, thereby inhibiting feeding, and some fibrous sheet materials, such as cardboard boxes, are not ground in a very effective manner. Therefore, there is much room for improvement, and there is still a substantial need for a small-scale or light-duty grinder that can handle a wide variety of commercial and industrial wastes as well as agricultural and feed products reliably, efficiently, and effectively.